Acousto-optic modulators have been utilized in prior art optical recorders for recording information on recording mediums sensitive to laser flux as shown, for example, in U.S. Pat. No. 3,922,485. In particular, this patent discloses a multifaceted polygon optical scanner which scans a modulated laser beam across a xerographic medium. The beam may be modulated by an acousto-optic modulator which is driven by a system which has, as one input, video input information which is to be reproduced. A motion blur problem can arise in those forms of optical data recorders in which there is significant relative movement between the recording medium and the focused writing beam. Reduction of motion blur by the use of very fast electro-optic modulators is possible, but that technique tends to be rather costly. State-of-the-art acousto-optic modulators are not effective in many potential applications because of the practical limitations in the rise time of the modulator which is imposed by the transit time of the acoustic wave front across the laser beam, thereby reducing or severely limiting the response of the modulator to high speed input video information.
Korpel U.S. Pat. No. 3,514,534 discloses a laser modulating and scanning system which utilizes a pair of acousto-optic devices to modulate and deflect a laser beam across an image screen. By positioning the acousto-optic devices apart a predetermined distance, a visible replica of the video information to be reproduced is formed in a manner such that the picture elements are immobilized on the screen.
An article by D. M. Robinson, "The Supersonic Light Control and its Application to Television with Special Reference to the Scophony Television Receiver", proceedings of the I.R.E., Vol. 27, pp. 483-486, August, 1939, discloses a system where a sound wave carries with it a replica of the video signal received during an immediately proceeding time interval and which is projected on a screen, a mirror polygon being utilized to move the whole image across the screen at the same speed in the opposite direction to immobilize the details on the screen.
A technique for providing a replica of the video signal carried by a sound wave to an optical recording system which utilizes rotating devices, such as a xerographic drum or an optical disc, as the reproduction medium and a simplified technique for immobilizing the image of the acoustic pulse at discrete areas at the writing surface to minimize image blur is disclosed in copending Application Ser. No. 920,314, filed June 28, 1978 now U.S. Pat. No. 4,213,158 and assigned to the assignee of the present invention. Although the technique described therein is satisfactory for most purposes, the frequency response thereof is limited. What is desired, therefore, is the high resolution system described in the aforementioned copending application which has an extended frequency response.
An improved Scophony system for processing bandlimited analog video signals is disclosed in copending Application Ser. No. 27,342, filed Apr. 5, 1979, now U.S. Pat. No. 4,253,725, and assigned to the assignee of the present invention. In accordance with the invention disclosed therein, a light profile of increased frequency is passed by the deflector of a Scophony scanner system by decentering the optical alignment of the system so that the light profile falls just within one edge of the deflector window. One advantage of this decentering of the optical alignment is an increased frequency response by the system due to transmission of only one sideband of the light profile, which in terms of a printing system, means increased resolution. However, this system is not responsive to a video binary digital bit stream which is the format utilized in many printers, including laser printers, and therefore has limited use in printer applications.